The invention lies in the telecommunications field. More specifically, the invention relates to a method for transmitting data from a first to a second private branch exchange in a private network. The invention also relates to a telecommunications system.
In order to allow subscribers in a telephone network to be offered specific service attributes, such as display of information about the calling subscriber, control data are also transmitted in addition to the wanted data, for example voice data. The control data include instructions to a switching center. One example of such an instruction to the switching center is call diversion, that is to say all calls going to a specific terminal shall be diverted to another terminal. This method is used in the public telephone network and in private branch exchanges which are used, for example, in businesses.
A protocol defines how connections are set up between the subscribers in a telephone network, which service attributes are offered in the telephone network, and how wanted data and control data must be transmitted. One example of such a protocol is the xe2x80x9cQSIGxe2x80x9d protocol. Connections between subscribers in different private branch exchanges are in this case routed via the public telephone network. In the process, one problem that arises is that the service attributes which are offered exclusively by the private branch exchanges and not by the public telephone network cannot be used, since the public telephone network does not offer the capability to transmit the required control data.
One known solution for this limitation is the use of a tie line between the private branch exchanges via the public telephone network. However, this solution has the disadvantage that the transmission capacity of the tie line is limited, and cannot be matched to the currently required transmission capacity. For a network with a number of private branch exchanges, which is called a private network, an optimum arrangement of the tie line can be found only with a high level of complexity. Any change to the number of private branch exchanges to be connected also requires adaptation to the arrangement of the tie lines. Furthermore, setting up such a private network is relatively costly.
It is accordingly an object of the invention to provide a method for interchanging data between private branch exchanges and a telecommunications system, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which allows using the service attributes of the private branch exchanges with little complexity and at low cost.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for transmitting data from a first private branch exchange via a computer network to a second private branch exchange, the method which comprises the following method steps:
splitting data to be transmitted from a calling subscriber of a first private branch exchange to a called subscriber of a second private branch exchange into wanted data and control data with a first converter, wherein the wanted data contain wanted information and connection set-up information, and the control data are data for controlling the second private branch exchange;
determining destination address information from the connection set-up information and identifying a receiver device;
converting, with a first switching unit assigned to the first private branch exchange, the wanted data and control data into data packets, and transmitting the data packets via a computer network to the receiver device designated by the destination address information;
receiving the data packets with a second switching unit assigned to the second private branch exchange, converting the data packets into wanted data and control data, and passing the data on to a second converter; and
joining the wanted data and the control data together with the second converter and forming data for further processing by the second private branch exchange.
In other words, each private branch exchange has access to a computer network which is used for transmitting data packets. The computer network is used to interchange the wanted data and control data between the private branch exchanges.
In accordance with an added feature of the invention, the connection set-up information is formulated on the basis of a number plan assigned to the first private branch exchange. The number plan contains subscribers of the private branch exchanges and a respective private branch exchange associated with each subscriber. All the subscribers of the private network are listed in the number plan, with the respective private branch exchange associated with them. Once a calling subscriber has dialed a number, the private branch exchange uses the number plan to check whether this number refers to a terminal of its own private branch exchange. If the number belongs to a terminal in another private branch exchange, it passes the wanted data and control data on to a converter. The primary example of wanted data are voice data.
The converter splits the data for the calling subscriber into wanted data and control data, defines destination address information with whose aid the data can be transmitted to a second converter, and passes the data on to a first switching unit. The first switching unit opens a connection to the computer network and uses the wanted data and control data to form data packets, which it transmits via the computer network to a second switching unit. The second switching unit joins the received data packets together again to form a wanted data stream and a control data stream, and passes the streams on to the second converter. The second converter joins the wanted data and control data together and transmits this data to the second private branch exchange connected to it, which can be controlled by the transmitted control data.
The method according to the invention allows any desired number of private branch exchanges to be combined to form a private network. In order to expand the private network, the number plan of the private network is expanded by the numbers of the exchange to be integrated, and this is notified throughout the entire private network.
In accordance with an additional feature of the invention, the computer network is the Internet or an Intranet and the data packets are generated according to the Internet Protocol IP. The Internet Protocol IP defines how the wanted data and control data are split into data packets and are transported, and defines a format for addresses of computers in the computer network. Thus, both the Internet and an Intranet can be used for the invention.
Four embodiments for interchanging data between the private branch exchange and the computer network are described in the following text. In a first embodiment, the private branch exchange contains the converter and the switching unit. The private branch exchange sends the control data to the computer network via a first logic link, and the wanted data via a second logic link. The same physical connection can be used for transmitting the data via the first and second logic links. This embodiment is suitable, in particular, for private branch exchanges where the number of calls to other private branch exchanges which are part of the private network is low.
In a second embodiment, the private branch exchange is connected to a switching computer, which passes the wanted data and control data on to the computer network. In this embodiment, the private branch exchange transmits the wanted data and control data via separate connections to the switching computer. The control data can be transmitted using a method which is defined by the known X.25 protocol. The wanted data can be transmitted using a telephone connection, for example an ISDN connection.
In a third embodiment, the tasks of the converter and of the switching computer are carried out by a common computer. The private branch exchange interchanges the wanted data and control data with the computer via a telephone connection. This computer splits the wanted data and control data and prepares them such that they can be transmitted by the computer network to the second private branch exchange. For example, communication between the private branch exchange and the computer can be carried out using a method which is described by the known QSIG protocol or another protocol for private networks, for example DPNSS or CorNet-N.
In a fourth embodiment, the functions of the converter and the communication with the computer network are respectively carried out by autonomous computers. The communication between the private branch exchange and the converter may be carried out, for example, using the method defined by the QSIG protocol. The control data can be transmitted from the converter to the switching computer using the method defined by the X.25 protocol or another protocol for connection-oriented data transmission, while the wanted data are preferably sent to the switching computer via a telephone connection.
The X.25 protocol describes a method for connection-oriented transmission of data packets. In this case, the data packets from a number of transmitters are transmitted by one multiplexer via one data line. It is feasible for the method for data transmission in accordance with the X.25 protocol to be adapted such that it is possible to dispense with the multiplexer, and to transmit the data asynchronously. One possible embodiment of such an adapted method is the insertion of control symbols for separating the data blocks. These data blocks are formed from the data packets using a method defined by the xe2x80x9cHigh Level Data Link Controlxe2x80x9d protocol, the HDLC protocol for short. The symbol xe2x80x9cStart of Text,xe2x80x9d STX for short, can be used, for example, for the start of the data block, and the symbol xe2x80x9cEnd of Text,xe2x80x9d ETX for short, for the end of the data block.
Furthermore, it is worthwhile for the converter to report the IP address of the second switching computer to the first switching computer. To do this, it is possible, for example, to store the IP address of the second switching computer in the address field of a data packet by means of which the X.25 connection is produced between the converter and the first switching computer. This avoids the need to keep and maintain in the switching computer tables for translating the X.25 addresses into IP addresses. In a preferred embodiment, the last four bytes of the address field are used for this purpose.
In addition, the method according to the invention can be expanded such that, if the data transmission does not take place via the computer network, the private branch exchange attempts to carry out the data transmission via another computer network or a tie line.
It is advantageous to expand the method according to the invention such that a calling converter is identified to a called converter. This allows a number of converters to be used in one private network. xe2x80x9cDirect Dialing Inxe2x80x9d numbers, or DDI numbers for short, may be agreed, for example, for this purpose. In a first embodiment, at least one DDI number is assigned to each converter. The calling converter sends this number, in addition to the wanted data and control data, to the called converter. This embodiment may be used when the first switching computer also sends the number of the calling converter to the second switching computer.
In a further embodiment, each combination of calling and called converters is assigned a DDI number. The calling converter translates the number which has been dialed by a subscriber into the DDI number for the called converter. The called converter thus uses the expanded number to identify the calling converter. The identification of the calling converter allows the called converter to set up a connection to the calling converter, in order to transmit control data to the calling converter.
With the above and other objects in view there is also provided, in accordance with the invention, a telecommunications system with a plurality of subscribers, comprising:
a first private branch exchange, a second private branch exchange, and a computer network for transmitting data from the first private branch exchange to the second private branch exchange;
each the private branch exchange having a number plan listing all subscribers of the telecommunications system and a respective the private branch exchange assigned to each subscriber;
a first converter assigned to the first private branch exchange, the first converter:
splitting the data to be transmitted from a calling subscriber of the first private branch exchange to a called subscriber of the second private branch exchange into wanted data with wanted information and connection set-up information according to the number plan and into control data for controlling the second private branch exchange; and
determining destination address information identifying a receiver device with the connection set-up information;
a first switching unit assigned to the first private branch exchange for converting the wanted data and the control data into data packets and for transmitting the data packets via the computer network to the receiver device designated by the destination address information;
a second switching unit assigned to the second private branch exchange for converting the data packets received from the first switching unit into wanted data and control data; and
a second converter assigned to the second private branch exchange for joining the wanted data and the control data converted by the second switching unit and forming data for further processing by the second private branch exchange.
The computer network used in the system is the Internet or an intranet.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in Method and telecommunications system for transmitting data from a first to a second private branch exchange, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.